Photoconductive device and method of making it



Patented Apr. 9, 1935 Q I I v tion from the state oi equilibrium prevailing in meta] may be reduced or isolated g w t UNITED STATES PATENT oFFlcE PHOTOCDNDUCTIVE DEVICE AND hIETHOD OF MAKING IT VilmosErvin Burg, Karlsruhe-Baden, Germany,

assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation cl Germany No Drawing. Application November 5, 1931, Serial No. 573,309. In Germany November 5,

Claims. (Cl. 201-63) My invention relates to light responsive devices Now, I have discovered that this drawback can of the photoconductive type, such as selenium, be overcome, and in accordance with my invehthalofide, and similar cells, and to methods of tion, in the preparation of the cells I add free making such devices. sulfur in amounts not over 1%, in which case The object of my invention is to provide photometallic additionasuch as silver, may under cer- 5 conductive cells which are of higher power and tain circumstances be dispensed with. However, capable of handling greater loads, which have additions -of metal as well as sulfur may be degreater sensitivity, particularly to red rays and sirable in some cases, as the'metal affects also which are in general an improvement on such the power of these suliured cells ina typical mancells heretofore used, and also to provide methods her, or ins ead of t e sulfuran'd m t ls. metallic m of making such cells; sulfides could be used for incorporation. It is In accordance with my invention the light senthus readily possible to build cells capable of sitive or photoconductive substance is improved handling currents of 50 milliamps and over. by the addition of tellurium or sulfur in proper It has been known for a long while that metals amounts, or silver may be added' by an improved especially silver may be added in comparatively 1 method, and improved electrode material with slight amounts, say, upto ;%.t0 selenium, for which the photoconductive substance is in conthe purpose of diminishing its inertia in action. tact is provided. It is likewise known to use, in lieu of silver or It is known in the art that selenium or thalosimilarly acting metals, the selenides of the met flde cells have inherently a certain sensitiveness als. However, it hasgien discovered that by the to red rays which, in fact, is far higher than that methods heretofore d it is impossible to inof the alkali photo cell, and this property has led sure a uniform distribution of these extremely to the tendency to replace alkali cells which opersmall additions throughout the entire mass of ate in some cases unsatisfactorily because of their the selenium. In fact, perfect homogeneity of lack of reponsiveness to red rays, by selenium or the mass and thus readily reproducible and conother devices more responsive to red rays. stant light responsive substances are unattain- According to the present invention I have able in this manner. found that by suitable additions the sensitivity to Now according to my invention this drawback red rays-of selenium, thallium compounds and is obviated and light responsive substances of the like in light-responsive devices can be markparticularly high sensitivity and load-carrying edly increased by suitable additions, and in accapacity are obtained by making the metallic ad.- cordance with my invention 1 add to the light ditions in the form of metal salts which are soluresponsive substance in these devices, over and his in some suitable solvent, such as water or above known admixtures, or even without other organic solvents, these solutions being added to admixtures, the metal tellurium or compounds, the selenium to make a paste or dough. It is in such as tellurides, oi the metal tellurium, though this way an easy matter to uniformly grind to- 35 in amounts not over 5%. By these additions I gether with the selenium even very small quantip d a light p s v su tan p rt ula ly ties of additions in the iorm of a dilute solution, Suitable for use in the manufacture of h h p w and to thereupon evaporate to complete dryness cells capable of standing a load of 5 watts and with onstant tirring the selenium dough or even more- I paste. Among the salts preierably used for this I11 is also known in the art that Silver in Small purpose are nitrates such as silver nitrate or else quantities i incorporated in light-Sensitive nickel chloride, or the metallic intermediates revices such as selenium cells or the like, with the sulting in th G m d th lik object of causing a more rapid change or transi- Either before gt evamm t eg th the resistance in unilluminated state to the state pounds by suitable physical t t t, such a resulting from irradiation, in other words, in orheating or by 1 t t t such as t ts der to reduce the sluss h s of th cell. but ment with suitable gases, solutions, or the like.

that cells thus made with silver additions exhibit In th manufacture selenium 11 thalgflde less sensitivity. At the same time it is found that cells d t l k in hi th mint responsive the cells thus manufactured with silver salt insubstance is in contact with electrodes metals corporation posses alsov a relatively low power, must be used'for the electrodes which will not particularly since it is dimcult to obtain cells by undesirably aflect the properties of the light the above method adapted to control currents responsive substances owing to and ass. conselarger than 20 milliamps. f quence or chemical re -actions. Themetals mostly and preferably used in the past are platinum; platinized or platinum plated wires, or alloys of noble metals. In addition a number of commercial on technical alloys have been used for the electrodes, but have caused more or less impairment in the quality of the cell as a result of chemical re-actions.

In accordance with my invention these disadvantages are avoided by making the electrodes especially wires or contact surfaces of tungsten or molybdenum or alloys thereof, which have proved to be highly suitable because between these electrodes and. the photoelectric substance of the cell no re-action at all takes place, or else the re- 15 action is of such a nature that the quality of the cell is not at all impaired as a consequence of the re-action. I have furthermore discovered that nickel, cobalt, manganese and chromium or their alloys may be used as electrodes that are advantageous for the same reasons.-

Claims:

1. A light-sensitive device comprising selenium containing metallic sulfides.

2. The method of incorporating in selenium a small amount of additive metal which consists in mixing with the selenium a solution of a readily decomposable inorganic compound of the additive metal, and decomposing said compound to produce said additive metal in finely divided form.

3. The method of incorporating in selenium a small amount of additive metal which consists in mixing with the selenium a solution in an organic compound of the additive metal in solution, evaporating the mixture to dryness, and decomposing said compound to produce finely divided additive metal intimately and uniformly distributed throughout the selenium.

5. The method of incorporating in selenium a small amount of additive metal which consists in mixing with the selenium a readily decomposable compound of the additive metal in solution, evaporating the mixture to dryness, and decomposing said compound to produce finely divided additive metal intimately and uniformly distributed throughout the selenium and melting the selenium containing the additive metal.

VILMOS ERVIN BURG. 

